1. Field of the Invention
The present invention relates to a reflector, a reflector integrated with a polarizing film, and a reflector integrated with a polarizing film and a retardation film, that are used in liquid crystal display (hereinafter, referred to as LCD) apparatus.
2. Description of the Related Art
Conventionally, a TN type LCD, an STN type LCD, a two-terminal device type LCD, and three-terminal device type LCD are used as LCD apparatus. Among these display apparatus, a reflective type liquid crystal display apparatus requiring a polarizing film and a reflector is shown in FIG. 9. The reflector integrated with a polarizing film is constructed by forming an adhesive 2, a protective layer 3, a polarizer 4, a protective layer 3', an adhesive 2', and an interliner 5 on a reflector 1 as shown in FIG. 9. The reflector 1 is categorized into the following three types: a metal vapor deposition type in which a metal film 7 is deposited on a plastic film 6 as shown in FIG. 10; a layered type in which a metal foil 8 is pasted on the plastic film 6 by an adhesive 9 as shown in FIG. 11; and a coating type in which a metal paint 10 is coated on the plastic film 6 as shown in FIG. 12. The metal film 7, the metal foil 8, and the metal paint 10 are mainly made of aluminum. The three types of reflector will be described below in detail.
1. Metal vapor deposition type
A reflector is constructed by forming an aluminum thin film (the metal deposition film 7) having a thickness of 500-600 .ANG. (angstroms) by vapor deposition on a polyethylene terephthalate (PET) film (the plastic film 6) on which an unevenness is formed. The reflector is non-directional. With regard to the method to form the unevenness on the plastic film 6, the following methods are known: forming a film of a synthetic resin mixed with inorganics; sand-blasting the surface of the plastic film 6; hydro-honing; coating the surface of the plastic film 6 with a synthetic resin after a chemical processing as disclosed in Japanese Laid-Open Patent Publication No. 60-117281; or the like.
2. Layered type of metal foil 8 and the plastic film 6
(1) Layered type of aluminum foil (the metal film 8) and the plastic film 6:
This type of the reflector is produced as follows. The mat face of an aluminum foil is pasted on a PET film (the plastic film 6), and the glossy face of the aluminum foil is roughened by blasting a grainy substance, such as sand as disclosed in (Japanese Laid-Open Patent Publication No. 3-246502). Alternatively, instead of blasting a grainy substance, contact an embossing roll on the surface of the aluminum foil so as to roughen the surface can be used as disclosed in (Japanese Laid-Open Patent Publications No. 58-219526, and No. 3-246502).
(2) Layered type of aluminum film having hair lines (the metal foil 8) and the plastic film 6:
This type of reflector is produced by repeated rolling of an aluminum foil. The aluminum foil becomes very thin in the last step of the rolling process. Therefore, two sheets of aluminum foil are placed together and rolled, and then separated. The surface of the aluminum foil contacted with the roll is glossy and has a larger reflectivity. The surface contacted with the other aluminum foil becomes mat and has a smaller reflectivity. The mat surface of the aluminum foil (AA1100 or JIS 1N30) is pasted on a PET film (the plastic film 6) by the adhesive 9 so as to form a reflector. Since the reflector has fine concavities and convexities extending vertical to the rolling direction of the aluminum foil, the reflector has directionality in its reflective characteristics, and so the reflective surface may be dark depending on the viewing angles as disclosed in (Japanese Laid-Open Patent Publication No. 58-219526).
(3) Layered type of mat aluminum alloy foil (the metal foil 8) and the plastic film 6:
This type of reflector is produced as follows. An aluminum alloy containing a small amount of iron and manganese is rolled so as to produce a foil. Then, the foil is layered on a PET film with an adhesive between them. Smooth micro-projections are formed on the surface of the foil, and the foil is non-directional and glossy as well as disclosed in (Japanese Laid-Open Patent Publication No. 64-66687).
3. Coating type in which the metal paint 10 is coated on the plastic film 6
This type of reflector is produced as follows. An aluminum paint containing aluminum flakes (metal paint 10) is coated on a PET film (plastic film 6) so as to construct a reflector (Japanese Laid-Open Patent Publication No. 60-482). The reflector is non-directional.
The aluminum reflector described above do not have a sufficiently high glossiness. Therefore, when one of these reflector is integrated with a polarizing film or the like and pasted on a liquid crystal panel to make a display device, the display of the device becomes dark. Moreover, in the case of a black and white display, the background color becomes grayish white.
It is known that silver and gold, which are precious metals, have higher reflectivities than that of aluminum in the range of visible light wavelength (G. Hass: "Filmed Surface for Reflecting Optics", Journal of the Optical Society of America, vol. 45, No. 11, pp. 945-952, 1955). Use of silver or gold vapor-deposited film is described in Japanese Laid-Open Patent Publications No. 54-158253 and No. 60-117281. Use of silver foil is described in Japanese Laid-Open Patent Publications No. 2-149801 and No. 3-246502.
The metal used for the vapor-deposited metal film 7, the metal foil 8, and the metal paint 10 of the above-described conventional reflector contain mainly aluminum or aluminum alloy. These reflectors for a liquid crystal display using aluminum or aluminum alloy do not have a sufficient glossiness or diffuse reflectivity. The reflectors for a liquid crystal display using silver or gold, which have higher reflectivities than that of aluminum, are expensive since gold and silver are precious metals, so such reflectors are not for practical use.